Machine for confining a primary fluid by means of a secondary fluid in the vapor phase

ABSTRACT

The invention relates to a machine for confining a primary fluid by means of a secondary fluid whose boiling temperature is lower than that of the primary fluid. The machine includes, in particular, primary vapor cooling means comprising a heat exchanger (11) for exchanging heat between the primary vapor and the secondary fluid (12), which means are provided with orifices (15) for exhausting the secondary vapor into the inside of the tank (4) so that the hat exchanger ensures that the primary vapor condenses and that the secondary fluid vaporizes, thereby making it possible to obtain thermal self-stabilization inside the tank.

TECHNICAL FIELD

The present invention relates to the technical field of using asecondary fluid in the vapor phase to confine a primary fluid that isadapted to perform treatment, in the broad meaning of the term, onvarious parts or objects.

It is necessary to keep the primary fluid in a limited space wheneverthe fluid is of a dangerous nature and/or has a high purchase price. Byway of non-limiting example, the primary fluid may be perchloroethylene,trichloroethylene, any type of solvent, or a fluorocarbon type liquid.

An application of the invention lies, for example, in the field ofcleaning or degreasing parts or objects.

Another particularly advantageous application of the invention lies inthe technical field of mounting components in the broad sense, e.g.electronic, electrical, electromechanical, or mechanical type componentson a support by means of additional material deposited at pointsassociated with fixing pads of the components. More precisely, theinvention can be used in the technique of assembling components bypolymerization, in which the additional material is constituted by apolymer, or in the component soldering or reflow technique in which theadditional material is constituted by an alloy.

PRIOR ART

In such techniques, it is known in general to use a treatment machinethat includes a tank containing a liquid of the fluorocarbon type to bebrought to a boiling temperature by heater means so as to produce asaturated and inert primary vapor in an assembly or soldering zone,which vapor is at a temperature that is slightly higher than the meltingtemperature of the additional material. The assembly or soldering zoneis substantially defined between the level of the liquid and a coil usedfor condensing the primary vapor. The assembly or soldering zone isoptionally surmounted by a preheating or cooling zone in which thereexists a secondary vapor.

In its top portion, the tank includes a through opening that can beclosed by a cover and that is there to allow a support carryingcomponents to be assembled thereto to be inserted into the inside of thetank. Such a support is handled by a device that moves it and holds itsuccessively in the preheating zone, the soldering zone, and the coolingzone. Thus, after the support has been held in the preheating zone for adetermined length of time, the support is brought into contact with theprimary vapor to cause the latent heat of condensation of the vapor tobe transferred to the support and its associated components. This heatinput raises the temperature of the support and the components quicklyand uniformly to the temperature of the primary vapor, thereby causingthe additional material to melt and consequently, depending on thetechnique used, causing the components to be soldered or polymerized.

By way of example, patent application Ser. No. 90/07,603 describes sucha machine whose operation gives satisfaction in practice. Nevertheless,it should be observed that the secondary liquid is used is generally ofthe CFC type of the kind specified by the Montreal convention, andfuture use thereof is to be banned. Such a situation leads, moreparticularly, to two types of machine being used, one that operates witha single vapor phase, and another that operates with two.

A machine operating with a single vapor phase does not include apreheating or cooling zone constituted by a secondary vapor. Inaddition, the coil for cooling the primary vapor is omitted, withcondensation of the primary vapor being provided by a refrigerated beltlocated at the top portion of the tank. The parts are generallypreheated by infrared radiation. That solution presents drawbacks,insofar as cooling takes place in a non-inert ambient atmosphere thatcould harm the metallurgical quality of the soldering.

The other type of machine which operates with two vapor phases has asecondary vapor surmounting a primary vapor. The ban on CFCs means thata substitute secondary liquid is used, requiring the cooling fluid forcondensing the primary vapor to be replaced bythermostatically-controlled oil. Although that technique using two vaporphases ensures good metallurgical quality for soldering whilesimultaneously complying with standards for protecting the environment,it must be observed that controlling the temperature of the cooling oilturns out to be particularly difficult to achieve.

There is therefore a need to have available a machine which ensureseffective confinement of a primary fluid by using a secondary fluid inthe vapor phase, but of a kind that is not dangerous, and in whichtemperature control turns out to be particularly easy to perform well.

SUMMARY OF THE INVENTION

The invention therefore seeks to satisfy this need by proposing aprimary fluid confinement machine suitable for complying with standardsfor environmental protection and designed to make it easy to obtainthermal regulation of the temperature of the primary vapor inside thetank.

To achieve this object, the invention provides a machine for confining aprimary fluid by means of a secondary fluid whose boiling temperature islower than that of the primary fluid, the machine including at least onetreatment tank fitted both with heater means suitable for raising theprimary fluid to boiling temperature, in such a manner as to produce aprimary vapor in a utilization zone which is surmounted by coolingmeans, and secondly means for producing a secondary vapor from asecondary fluid, the secondary vapor occupying a preheating or coolingzone overlying the utilization zone.

According to the invention, the cooling means for cooling the primaryvapor are constituted by a heat exchanger for exchanging heat betweenthe primary vapor and the secondary fluid, the heat exchanger beingprovided with outlet orifices for expelling secondary vapor into theinside of the tank so that the heat exchanger condenses the primaryvapor and vaporizes the secondary fluid, thereby enabling thermalself-stabilization to be obtained inside the tank.

Another object of the invention is to provide a confinement machine thatmakes it relatively easy to switch from operating with two vapor phasesto operating with one, and vice versa.

To this end, the reservoir is provided both with a drain pipe fordraining the secondary fluid, which pipe is provided with a controlledvalve, and with a return pipe for returning primary fluid to the tankand itself fitted with a controlled valve, the valves of the drain pipe,the overflow pipe, and the tank return pipe being controlled so as toenable operation to switch from a "two-phase" mode of operation usingboth the primary and the secondary fluids to a "one-phase" mode ofoperation in which only the primary fluid is used, and back again.

Various other characteristics appear from the following descriptiongiven with reference to the accompanying drawings, which showembodiments and implementations of the invention as non-limitingexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section in elevation showing in its left and right portionstwo embodiments of a confinement machine of the invention that isadapted to soldering.

FIG. 2 is a fragmentary perspective view showing characteristic detailsof the invention.

FIG. 3 is a simplified hydraulic circuit diagram for explaining acharacteristic of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows an application of the invention to a vapor phase assemblymachine for mounting components 2 of any type, singly or in combination,on a support 1 in the broad sense. The components may be electronic,electrical, mechanical or electromechanical, and they are organized in amanner appropriate for taking on specific functions relating to theirintended application. In the example described herein, which relatesspecifically to the vapor phase reflow soldering technique, the support1 constitutes a printed circuit for receiving components 2 that arefixed thereon by means of an additional material which is constituted byan alloy. The assembly C constituted by the printed circuit 1 with thevarious components 2 is referred to below as a "card".

The machine has a protective structure 3 containing a treatment tank 4which is closed at its top portion by a cover 5. The treatment tank 4 isprovided externally with a thermal insulation jacket 6. The bottom ofthe tank is fitted with heater means 7 such as electrical resistanceelements. The resistance elements 7 are designed to raise a primaryliquid L to boiling temperature, which liquid in the example shown is ofthe fluorocarbon type, thereby enabling a primary vapor to be producedthat is saturated and inert, having a temperature that is slightlyhigher than the melting point of the alloy previously deposited on thecircuit 1 in association with fixing pads for the components 2. Theprimary vapor is intended to occupy a zone Za for use, assembly, orsoldering, which is defined substantially between the level of theliquid L and cooling means 8 of the invention which are described ingreater detail below.

The cooling means 8 are constituted by a heat exchanger 11 operatingbetween the primary vapor and a secondary liquid 12 which has a boilingtemperature lower than that of the primary liquid. The heat exchanger 11is constituted, at least in part, by the walls of a vessel, gutter, orreservoir 13 containing the secondary liquid 12.

As can be seen more precisely in FIGS. 1 and 2, the reservoir 13occupies a given level above the bottom of the tank 4 and extends aroundthe entire periphery thereof. The reservoir 13 includes at least oneheat exchange surface 11₁ constituted by the wall of the reservoirexposed to the inside of the tank. As shown in FIG. 2, the area of theheat exchange surface can be increased by making use of radiating fins11₂ carried by the wall 11₁ of the reservoir and placed on the inside ofthe tank, optionally together with fins carried by the opposite wall ofthe reservoir located on the outside of the tank (not shown).

In a first embodiment shown on the right-hand side of FIG. 1, thereservoir 13 has an inside wall 11₁ lying substantially in the sameplane as the inside wall of the tank.

In a second embodiment shown on the left-hand side of FIG. 1, the insidewall 11₁ of the reservoir projects beyond the plane containing theinside wall of the tank. To this end, a portion 11₃ of the bottom wallof the reservoir is exposed to the tank interior and projects inwardlyfrom the inside wall of the tank to perform a function that is describedbelow.

The reservoir is fitted with a cover 14 and it communicates with theinside volume of the tank 4 via outlet orifices 15 formed through theinside wall 11₁. The orifices 15 pass secondary vapor that comes fromvaporizing the secondary liquid 12. The secondary vapor is intended tooccupy a preheating or cooling zone Zr situated above the assembly zoneZa. Advantageously, the outlet orifices 15 have a total through sectionarea that is smaller than the surface area of the secondary liquidcontained in the reservoir 13, thereby building up pressure leading tothe secondary vapor being ejected and to said vapor extending to thecenter of the tank. A cushion of secondary vapor is thus created thatachieves effective confinement of the primary liquid.

Preferably, the cover 14 is organized to recover condensed secondaryvapor. For example, the cover 14 is provided with a rim 16 thatco-operates with the inside wall of the tank to define a recoverychannel which communicates with the reservoir via through openings 17.In an embodiment shown in FIG. 2, provision may be made for the insidewall 11₁ to be provided with a gutter 18 that also serves to recovercondensed secondary vapor.

The reservoir 13 includes a coil 19 thereabove for condensing thesecondary vapor. In conventional manner, the top portion of the tank 4is fitted with a cooling band 20 located above the coil 19 so as toensure practically complete condensation of residual vapor and limitconsumption of liquid.

The machine described above operates as follow.

When the heater means 7 are put into operation, the primary liquid Lbegins to vaporize. A portion of the primary vapor condenses on thesurfaces of the heat exchanger 11. The walls of the reservoir 13 thustransfer heat to the secondary liquid and its vapor is expelled into thepreheating or cooling zone Zr via the outlet orifices 15. It should beobserved than an increase in the level of the primary vapor gives riseto an increase in the surface area which is effective for heat exchange,thereby giving rise to a corresponding increase in the emission ofsecondary vapor. The increase in secondary vapor emission serves toincrease the thickness of the secondary vapor cushion, thereby loweringthe level of the primary vapor. The effect of this lowering is to reducethe surface area that is effective for heat exchange, thereby decreasingthe emission of secondary vapor. The decrease in the thickness of thecushion of secondary vapor leads to an increase in the level of theprimary vapor, and thus to an increase in the heat exchange area. Theabove-described process continues until it has stabilized thermally. Asa result, the machine of the invention makes it possible to achieveself-regulation or self-stabilization of temperature inside the tank,while simultaneously ensuring effective confinement of the primary vaporinside the tank by means of the cushion of secondary vapor.

It should be understood that the heat exchange area of the heatexchanger adjusts automatically to the amount of excess heat to beremoved as produced by the heater means 7. The heat exchanger area thusvaries between zero at the bottom of the reservoir 13 and a maximumvalue corresponding to the level occupied by the secondary liquid 12inside the reservoir. It should be observed that in the embodiment shownon the left-hand side of FIG. 1, the heat exchange area varies between amaximum value corresponding to the maximum height occupied by thesecondary liquid inside the reservoir 13 and a constant minimum valuedefined by the bottom wall 11₃ of the reservoir which projects from theinside wall of the tank. In general, it should be considered that theheat exchanger 11 must have a heat exchange area of dimensions adaptedto absorb the heat conveyed by the primary vapor as obtained when theheater means are operating at maximum power. In this respect, in theevent of a failure, provision is made for a temperature probe 22 (FIG.2) mounted on the reservoir 13 and connected to means adapted to stopoperation of the heater elements 7 whenever the temperature of the probereaches a value that corresponds substantially to the boiling point ofthe primary vapor.

The level of the primary vapor depends on the power delivered by theheater means 7 and on the heat exchange area on the heat exchanger 11.Additionally, provision may be made for the reservoir 13 to be fittedwith means for cooling the secondary liquid 12. By way of example, thesecooling means may be constituted by a coil 12a placed in the reservoiror by a cooling jacket (not shown) surrounding the reservoir.

The machine of the invention also offers the advantage of being capableof switching easily from operating with two vapor phases to operatingwith one phase only. As can be seen more clearly from FIG. 3, thereservoir 13 is provided with a secondary liquid feed pipe 24 itselffitted with a controlled valve 25 and connected to a pump 26 in turnconnected to a return or secondary fluid source 27 for the secondaryliquid 12. The outlet pipe from the return or source 27, situatedupstream from the pump 26, is fitted with a controlled valve 28.

The reservoir 13 is also provided with an overflow pipe 30 that sets themaximum level of secondary liquid 12 inside the reservoir 13. Theoverflow pipe 30 leads to the return or source 27 and it is providedwith a controlled valve 31. The reservoir 13 includes a drain pipe 32that leads to return or source 27 and that is provided with a controlledvalve 33. The reservoir 13 is also provided with a pipe 34 fitted with acontrolled valve 35 and serving to provide communication between thereservoir 13 and the inside of the tank 4.

When operating with two phases, the valves 33 and 35 are closed whilethe valves 25, 28, and 31 are open, with the pump 26 being switched onso as to feed secondary liquid to the inside of the reservoir 13.

When switching from operation with two vapor phases to operation withone phase only, the heater elements 7 are switched off as is the pump26. The valve 33 in the drain pipe is opened until all of the secondaryliquid 12 contained in the reservoir has been removed therefrom. Thevalves 25, 31, and 33 are closed and the valve 35 of the pipe 34 forreturn to the tank is opened. During operation using a single vaporphase, the reservoir 13 recovers primary vapor condensate which isreturned to the inside of the tank 4 via the pipe 34.

In order to switch from operation with a single vapor phase to operationwith two vapor phases, the heater means are switched off and the valve35 is closed. The valves 31, 28 and 25 are opened and the pump 26 isswitched on to fill the reservoir 13 with the secondary liquid. Theheater means 7 are then switched back on.

As can be seen from the above, the machine of the invention makes iteasy to switch from operation using a single vapor phase to operationusing two vapor phases, and vice versa. The machine also has theadvantage of enabling the primary liquid to be purified. To do this, thedrain pipe 32 must be provided with a branch connection having acontrolled primary fluid regenerator valve 36 leading to a secondaryfluid regenerator vessel 37 that is reserved for the primary liquid L.The outlet from the vessel 37 is connected to the pump 26 and is fittedwith a controlled valve 38. After the secondary liquid has been emptiedfrom the reservoir 13, primary liquid regeneration consists in closingthe valves 25, 31, 35, and 28, and opening the valves 33, 36, and 38.The heater elements 7 are switched on until the temperature measured atthe top level of the tank 4 reaches the boiling temperature of theprimary liquid. After the heater means 7 have been switched off, thetank 4 can be cleaned. Thereafter, the valves 33, 31, 36, and 28 areclosed while the valves 25, 35, and 38 are opened. The pump 26 isswitched on so as to transfer the purified primary liquid contained inthe vessel 37 into the tank 4 via the reservoir 13 and the return pipe34.

According to a characteristic of the invention, provision may have madefor the reservoir 13 to be at least one liquid injector 40 above thereservoir. As can be seen in FIG. 3, the injector point 40 is connectedto the outlet of the pump 26. The function of the injector 40 is toinject fine droplets of a cold liquid at a card that is in the processof cooling. The card is thus dried by lowering the boiling point of theliquid condensed thereon, thereby making it possible to acceleratecooling. Evaporation of the liquid uses up a large amount of the heatcontained in the card. It should be observed that the quantity of liquidinjected also makes it possible to control the rate of cooling.

Cooling by injecting liquid and evaporating it serves to reduce coolingtime, and consequently to improve the metallurgical quality of thesoldering. During operation with two vapor phases, this coolingtechnique is implemented more particularly by feeding the injector 40with the secondary liquid. For cooling operation, the valves 25, 35, 36,and 38 are closed while the valves 31 and 28 are open. The valve 33 isopened intermittently so as to maintain the secondary liquid in thereservoir 13 at a given level.

SUITABILITY FOR INDUSTRIAL APPLICATION

In the above description, the invention relates to a machine that isadapted more particularly to soldering parts by means of a primaryliquid L which is confined by a secondary vapor. It should be understoodthat the invention relates in more general manner to any machine havingone or more tanks enabling a vaporized or unvaporized primary fluid tobe confined by means of a secondary fluid in the vapor phase, with thenature of the primary fluid being appropriate for performing treatmenton parts or objects of various kinds. By way of example, the primaryfluid may be adapted to clean or degrease and it may be constituted byany type of solvent, including fluorocarbon liquids. Naturally, theboiling point of the secondary fluid must be lower than that of theprimary fluid, and the temperature difference must be sufficient toenable the phases to be separated. Also, the secondary fluid is of aninert character, being non-flammable, non-explosive, and non-toxic.

The invention is not limited to the examples described and shown andnumerous modifications can be applied thereto without going beyond theambit of the invention.

I claim:
 1. A machine for confining a primary fluid by a secondaryfluid, comprising:a treatment tank (4) including a lower area and atleast one generally vertical wall extending upwardly from said lowerarea for containing a primary fluid in liquid and vaporized forms; aliquid primary fluid (L) in the tank lower area; a heater (7) in thetank or area for heating liquid primary fluid in the tank to its boilingtemperature to produce a primary vapor of vaporized primary fluid in thetank above the liquid primary fluid; a utilization zone (Za) above theliquid primary fluid in the tank for receiving primary vapor uponvaporization of the primary fluid; a cooling system (8) above theutilization zone within the tank, the cooling system including areservoir container (13) defined by at least generally vertically andgenerally horizontally extending walls (11₁,11₃) exposed to the tankinterior and a liquid secondary fluid (12) contained in the reservoir,said liquid secondary fluid having a lower boiling temperature than saidliquid primary fluid; a preheating/cooling zone (Z_(r)) in the tanklocated above the utilization zone and adjacent the reservoir; saidreservoir including heat exchanger structure for exchanging heat betweenheated primary vapor in the tank and secondary fluid in the reservoir bytransfer of heat from the primary vapor to the liquid secondary fluid inthe reservoir, and outlet orifices (15) for discharging secondary fluidvapor vaporized by such heat exchange into the preheating/cooling zone;whereby primary vapor in the preheating/cooling zone heats and vaporizesliquid secondary fluid in the reservoir via the heat exchanger to causedischarge of secondary fluid vapor into the preheating/cooling zone tocool and condense the primary vapor in a continuous manner to therebyeffect self-stabilization and containment of the primary vapor in thetank below the preheating/cooling zone.
 2. A machine according to claim1, wherein said reservoir generally horizontal wall (11₃) projectsinwardly from the tank vertical inner wall towards the tank interior atthe preheating/cooling zone.
 3. A machine according to claim 1,including a source of secondary fluid and a secondary fluid supplyconduit (24) in communication with the reservoir, and an overflowconduit (30) having an input connected to the reservoir so that thelevel of secondary fluid in the reservoir may be maintained at aconstant level at the overflow conduit inlet upon flow of secondaryfluid from the source to the reservoir; a secondary fluid flow inducingdevice (26) for causing such flow; and a selectively controllableoverflow valve (31) in the overflow conduit arranged to control returnflow through the overflow conduit;whereby an operating level ofsecondary fluid in the reservoir may be established and maintained toprovide a heat exchanger area in the heat exchanger determined by saidoperating level.
 4. A machine according to claim 1, wherein said heatexchanger includes a heat exchanger area that is effective to condenseprimary vapor in the preheating/cooling zone when the heater is fullyoperational.
 5. A machine according to claim 1, wherein the reservoirincludes a cover (14) arranged so as to collect condensed secondaryfluid.
 6. A machine according to claim 5, wherein said reservoirincludes a gutter (18) arranged so as to collect condensed secondaryfluid, said gutter extending generally towards the tank interior.
 7. Amachine according to claim 1, including a secondary fluid cooler in thereservoir arranged to cool the secondary fluid.
 8. A machine accordingto claim 1, including a temperature probe in the reservoir and a centraldevice for controlling operation of the liquid primary fluid heater,said control device arranged so as to be responsive at least to a presethigh temperature sensed by the temperature probe.
 9. A machine accordingto claim 3, including a drain pipe (32) in communication with saidreservoir; a selectively operable drain valve (33) in said drain pipefor controlling flow in the drain pipe; a return pipe (34) having aninlet in communication with said reservoir and an outlet incommunication with the lower end of said tank; a selectively operablereturn valve in said return pipe for controlling flow in the returnpipe; said overflow pipe, overflow valve, drain pipe, drain value,return pipe and return valve being arranged such that upon selectiveopening and closing of said valves, the reservoir may be selectivelydrained of liquid secondary fluid and liquid primary fluid in thereservoir may be returned to the lower area of the tank, whereby themachine may function selectively as a "two-phase" or "one-phase"machine.
 10. A machine according to claim 1, including a liquidsecondary fluid injector located above the reservoir.
 11. A machineaccording to claim 9, including a primary fluid regeneration vessel(37), said drain pipe providing communication between said reservoir andsaid vessel; and a selectively operable primary fluid regenerator valve(36) in said drain pipe, whereby vaporized primary fluid condensed inthe reservoir may be regenerated.
 12. A machine according to claim 1,wherein the total flow area of said outlet orifices is less than thesurfaced area of the liquid secondary fluid, whereby, upon vaporizationof secondary fluid at its surface, the secondary fluid vapor ispressurized in the reservoir to cause ejection of the secondary fluidvapor through the orifices.